1. Field of the Invention
The present invention relates to target object detection and tracking, and more particularly, to a system and method for determining the location, including altitude, of a target object.
2. Discussion of the Related Art
The detection and tracking of a target object has typically been accomplished with radio detection and ranging, commonly known as radar. Radar emits electromagnetic energy and detects the reflected energy scattered by the target object. By analyzing the time difference of arrival (TDOA) and the direction of the reflected signal, the location of a target object can be discerned. By analyzing the frequency shift of the energy beam due to the Doppler effect, moving targets are differentiated from stationary objects.
Radar is typically an active device including its own transmitters and receivers. Signals sent by the transmitters are typically of two typesxe2x80x94pulse beams, or continuous wave.
A pulse beam transmitter generates intermittent signals with a specified delay between each signal. The delay between the pulsed signal provides the radar system a listening period to detect reflections from target objects. A pulse beam radar system determines the range of a target object by observing the TDOA, allowing the system to calculate the total distance traveled by the signal to and from the target object.
A continuous wave transmitter provides a constant, uninterrupted signal. A continuous wave radar system must detect reflected signals while it also broadcasts its direct signal. The continuous wave radar system relies on the Doppler effect to determine a target object""s radial velocity to the receiver. An unmodulated continuous wave radar system is incapable of determining the range of an object. This is so due to its inability to mark the time a signal was sent and received; thus, it is unable to observe a TDOA in the signal. Whereas, a modulated or coded continuous wave provides a way to determine when a specific section of the signal was sent and received. With a marked signal, a system is able to determine the TDOA, allowing the determination of the range of a target object.
The electromagnetic radiation used in a radar system may be of any frequency, or, as the continuous wave example above illustrates, of varying frequencies, as long as it is of sufficient signal strength to provide a detectable reflected signal. Due to various advantages, microwaves are primarily used in modern radar systems. Microwaves are particularly well suited for radar due to their lobe size, the distance between the half-power points of the signal. Beam widths of a microwave signal are on the order of 1 degree, or just a few centimeters in cross-section, allowing for accurate determination of angles with moderate receiver sizes.
Radar systems also come in various receiver/transmitter configurations, such as Monostatic, Bistatic, and Multistatic. Monostatic systems combine the receiver and transmitter. Noise and system integration issues are inherent in such a system. Furthermore, a transmitter broadcasting a detectable signal that is co-located with the receiver clearly presents a disadvantage in a military application.
Bistatic radar systems separate the receiver and transmitter from one another by significant distances. In a military application the separation of the transmitter and receiver reduces the possibility of destruction of both the transmitter and receiver if enemy forces detect the location of the transmitter. A bistatic radar system typically calculates the location of a target object by determining the distances between the transmitter, target, and receiver, known as the bistatic triangle.
Multistatic radar systems are similar to bistatic systems in that the transmitters and receivers are placed a distance apart. The difference is that multistatic systems implement multiple receivers and/or transmitters, which are coordinated to monitor a specific area.
Elevation calculation estimates made by radar systems are generally accomplished in one of two methods, sequential lobing or simultaneous lobing. Sequential lobing involves generating a sequence of beams at varying angles of elevation. The proportion of the reflected signals from each beam allows the elevation angle of the object to the receiver to be determined. The altitude of the target object is then calculated from the angle of elevation and the range of the target object.
Calculations made by a sequential lobing system are complicated when attempting to determine the elevation of a moving target. The sequential nature of this type of lobing system allows a moving target to change position between the successive lobes. Additionally, at microwave frequencies, an object such as an airplane is a few thousand wavelengths in size. Such a complex object, notwithstanding movement, will provide a wide range of scattering cross-sections for beam reflection.
Simultaneous lobing, also known as mono-pulse, reduces the complexities associated with a complex and moving target by broadcasting two or more beams simultaneously. These beams are known as the difference and sum beams. The simultaneous lobing system computes the ratio, providing a linear measurement between 1 and xe2x88x921, of the two or more beams to determine the elevation angle at which the object is located.
Elevation angles calculated by radar systems are always a derived, rather than a measured quantity. The accurate calculation of height from microwave radar must always take into account the location and orientation of the radar antenna, the curvature of the earth, the refractive properties of the atmosphere, and the reflective nature of the earth""s surface.
Furthermore, weather and humidity will also create variations in measurements due to the refraction created by moisture in the air. For example, clouds and/or rain will bend or distort the direction of the direct beam, as well as the reflection from the target object.
A factor further limiting accuracy in the detection and tracking of a target object is the interference effect patterns generated by transmitters of any electromagnetic signal. The interference effect patterns are the combination of signals broadcast by a transmitter and signals broadcast by the transmitter and reflected by the surrounding terrain. Due to the additional distance traveled by the signals reflected by the terrain they combine with the direct signals creating a combined signal that has been changed by phase differences of the signals.
These and other deficiencies exist in current object detection and tracking systems. Therefore, a solution to these problems is needed, providing an object detection and tracking system specifically designed to more accurately calculate the altitude of a target object.
Accordingly, the present invention is directed to a tracking and detection system and method.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof, as well as the appended drawings.
In one embodiment the invention comprises a system for detecting and tracking the location of a target object using signals transmitted by one or more independent transmitters, including an antenna for receiving the transmitted signals, a signal processing subsystem connected to the antenna for generating signal data by processing the signals received by the antenna, an object location processing subsystem connected to the signal processing subsystem for calculating target data including the location of the target object based on the signal data received from the signal processing subsystem, and is capable of calculating altitude data of the target object from signal data including signal data from one or more signals received by the antenna of an interference effect pattern from the one or more transmitters reflected by the target object, and a display subsystem for receiving target data from the object location processing subsystem and selectively displaying the target data of the target object.
In another embodiment, the invention comprises a system for detecting and tracking the location of a target object using signals transmitted by one or more independent transmitters, comprising an antenna for receiving the transmitted signals, a signal processing subsystem connected to the antenna for generating signal data by processing the signals received by the antenna, an object location processing subsystem connected to the signal processing subsystem for calculating target data including the location of the target object based on the signal data received from the signal processing subsystem, and is capable of calculating the location of the target object by calculating the intersections of geometric shapes associated with the three or more transmitters, and a display subsystem for receiving target data from the object location processing subsystem and selectively displaying the target data of the target object.
In a further embodiment the invention comprises a system for detecting and tracking the location of a target object using signals transmitted by one or more independent transmitters comprising, an antenna for receiving the transmitted signals, a signal processing subsystem connected to the antenna for processing the received signals, an object location processing subsystem connected to the signal processing subsystem for calculating target data including the location of the target object based on the signal data received by the signal processing subsystem, and is capable of selectively calculating altitude data of the target object by using signal data from an interference effect pattern of one or more transmitters or by calculating the intersections of geometric shapes associated with three or more transmitters, and a display subsystem for receiving target data from the object location processing subsystem and selectively displaying the target data of the target object.
In another embodiment the invention comprises a system for detecting and tracking the location of a target object, comprising, one or more transmitters for transmitting signals, an antenna for receiving the transmitted signals, a signal processing subsystem connected to the antenna for processing the received signals, an object location processing subsystem connected to the signal processing subsystem for calculating target data including the location of the target object based on the signal data received by the signal processing subsystem, and is capable of selectively calculating the altitude data of the target object by using signal data from an interference effect pattern of one or more transmitters or by calculating the intersections of geometric shapes associated with three or more transmitters, and a display subsystem for receiving target data from the object location processing subsystem and selectively displaying the target data of the target object.
In a further embodiment the invention comprises a method for detecting and tracking the location of a target object using signals transmitted by three or more transmitters, comprising the steps of receiving direct signals broadcast by the three or more transmitters, receiving reflected signals broadcast by the three or more transmitters and reflected by the target object, calculating a geometric shape associated with each of the three or more transmitters, and calculating the location of the target object using the geometric shapes.
In a further embodiment the invention comprises a method for detecting and tracking the location of a target object using signals transmitted by one or more transmitters, which form an interference effect pattern by the combination of a signal broadcast by the transmitter and a signal broadcast by the transmitter and reflected by the surrounding terrain, comprising the steps of receiving one or more signals broadcast by the one or more transmitters, receiving one or more reflected signals broadcast by the one or more transmitters and reflected by the target object, the reflected signal being modified by the interference effect pattern, and calculating the location of the target object using the direct signal and the reflected signal as modified by the interference effect pattern.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.